Learn Hardcore Polish: To jest łóżko, które kupiłem w listopadzie. - This is the bed that I bought in November.

To jest literally means “this is” (or “that is” in some contexts). It’s a fixed phrase used to introduce or point at something. The word to here is a neuter demonstrative pronoun and is always used in To jest … regardless of the gender or number of the noun you’re introducing.

You do not say Ten jest or Ta jest in this construction—only To jest.

Why is there a comma before które? Do I always need a comma before relative clauses in Polish?

Yes. In Polish, any clause introduced by a relative pronoun (takim jak który, która, które, którzy, których) is set off by a comma. So you always write
To jest łóżko, które kupiłem w listopadzie.
The comma marks the start of the subordinate (relative) clause.

What is które and how do I choose the correct form of który (który, która, które, etc.)?

Który means “which” or “that” and agrees in gender, number, and case with its antecedent (the noun it refers to).

Gender: masculine/feminine/neuter
Number: singular/plural
Case: depends on its role in the relative clause

Here, łóżko is neuter singular, and inside the clause it’s the direct object of kupiłem, so it’s in accusative. The neuter singular accusative form of który is które (which happens to look the same as the nominative).

Why is it kupiłem and not kupiłam?

Past-tense verbs in Polish agree with the speaker’s gender (and number).

A male speaker says kupiłem
A female speaker says kupiłam

Since the sentence uses kupiłem, we know the speaker is male.

Why do we say w listopadzie instead of we listopadzie or na listopadzie?

The preposition w (“in”) takes the locative case.
Listopad (November) in the locative becomes listopadzie.

So w listopadzie = “in November.” You never say na listopadzie for months, and w does not change to we because listopadzie starts with a consonant cluster (no special e is needed).

How do I pronounce łóżko and kupiłem, and where is the word stress?

Polish stress is almost always on the penultimate (second-to-last) syllable.

łóżko: two syllables ['wuʐ.ko], stress on ŁÓŻ
kupiłem: three syllables [kuˈpʲi.wɛm], stress on PI

Pronunciation tips:

ł = English w
ó = u sound
ż = zh as in “measure”

Can I say łóżko, co kupiłem w listopadzie instead of using które?

No. In standard Polish, co is used for relative clauses only when the antecedent is a pronoun like wszystko (“everything”), coś (“something”), or nic (“nothing”). For nouns (like łóżko) you must use który/która/które, so łóżko, które kupiłem… is correct.

Is it possible to omit To jest and just say Łóżko, które kupiłem w listopadzie as a complete sentence?

Not in everyday speech. Without To jest, you end up with a noun phrase, not a full sentence. You could use it as a title or bullet-point note (like a caption), but to make a complete sentence in conversation you need To jest (or another verb).

How would this sentence change if I were talking about multiple beds?

You’d switch to the plural forms of the demonstrative, noun, relative pronoun, and verb gender/number marker:
To są łóżka, które kupiłem w listopadzie.

To są instead of To jest
łóżka (plural of łóżko)
które remains the same in neuter plural accusative/nominative
kupiłem stays kupiłem (1st sg. past) because the speaker is still talking about “I” buying them